Extraction and chromatographic media and processes, which can be broadly described as separation science, are known in the art. They provide a means of isolating, separating, and analyzing mixtures of solutions by selective adsorption on materials such as nylon, alumina, silica, and bonded silica. The process is based on differences in the distribution ratios of the components of mixtures between a mutually immiscible mobile and a fixed stationary phase. In thin layer chromatography, it is known to use thin films, such as silica mixed with a binder (e.g. calcium sulfate) adhered to glass for the separating vehicle. In particular, there are formed isolated spots or bands which can be separated mechanically and further examined.
U.S. Pat. No. 4,153,661 discloses a method of making a polytetrafluoroethylene composite sheet comprising a PTFE matrix with particulate material, which is substantially insoluble in water, dispersed therein. The resulting sheet is extremely pliable, akin to doe skin. It is said to be useful as an electronic insulator or a semi-permeable membrane
U.S. Pat. No. 4,373,519 discloses a composite wound dressing comprising a PTFE matrix with water-swellable hydrophilic absorptive particles enmeshed in the matrix, and, optionally, a partially occlusive film coated on one surface of the matrix. It is disclosed that the particulate material can account for from 40 to 90% by weight of the total composition, of which up to 50% can be inert property modifier particles. Examples of property modifier particles include silica, kaolin, talc, bentonite, vermiculite, etc. The sheets are described as conformable and chamois-like.
U.S. Pat. Nos. 4,565,663 and 4,460,642, which are related to U.S. Pat. No. 4,373,519, disclose water-swellable composite sheets having a PTFE matrix in which water-swellable hydrophilic absorptive particles are enmeshed. As in U.S. Pat. No. 4,373,519, the water-swellable particulate can account for from 40 to 90% by weight of the total composition, of which up to 50% by weight can be inert property modifier particles, e.g. silica. The sheets are described as conformable and chamois-like. It is disclosed that they can be used as chromatographic materials. It is also disclosed that certain water-swellable cation exchange resins can be used in chromatographic applications.
U.S Pat. No. 4,810,381, U.S. Pat. No. 4,906,378, and U.S. Pat. No. 4,971,736 disclose composite articles comprising a PTFE fibril matrix in which is enmeshed non-swellable particulate. The articles are useful in chromatographic applications. Up to 30 weight percent of total particulate can be property modifier particles which include polymethacrylates, styrene-divinylbenzene copolymers, and silica coated with polyacrylamide. Stacked layers of identical composition are disclosed as a means of increasing path length.
Hagen et al., Analytical Chimica Acta, 236 (1990) 157-164, disclose a method using hydrophobic C.sub.8 - and C.sub.18 -bonded silica particles enmeshed in a PTFE membrane as an alternative to using particle packed columns for solid phase extraction (SPE) applications.
Highly crosslinked copolymeric particles of styrene and divinylbenzene (XAD.TM. nonionic polymeric adsorbents) and highly crosslinked methacrylic copolymeric particles (Amberchrom.TM.) polymeric adsorbants are available commercially from Supelco, Inc., Bellefonte, Pa. Octadecyl-bonded silica particles, another type of adsorbent, are available from Varian Sample Preparation Products, Harbor City, Calif.